The present disclosure relates to a fixing device fixing a toner image onto a sheet and an image forming apparatus including this fixing device.
Conventionally, an image forming apparatus of an electrographic manner, such as a copying machine or a printer, includes a fixing device fixing a toner image onto a sheet.
For example, the fixing device may include an endless belt (a fixing belt) coming into contact with a roller and rotating by following the roller, and a heat source arranged inside any one of the roller and the endless belt. The fixing device includes a pressuring member (a pressing member) pressuring the endless belt to the roller inside the endless belt. The pressuring member includes a sliding layer at a side coming into contact with the endless belt. The sliding layer includes at least two or more layers to hold a lubricant.
Alternatively, the fixing device may include a heating roller and a fixing belt circumscribing each other so as to form a fixing nip, a rubber pressing member, a resin pressing member, a sliding sheet, and an electric conductive sheet. The electric conductive sheet is arranged between the sliding sheet and a contact portion of the rubber pressing member and the resin pressing member.
In the above-mentioned fixing device, in order to prevent damage of a pressuring roller and a driving part thereof, a sliding layer of a roller (the pressuring roller) is made to hold the lubricant. Accordingly, friction resistance of the pressuring roller and the fixing belt is reduced and load torque of the fixing belt is reduced. Moreover, the fixing belt may be configured so that the above-mentioned sliding sheet (a sliding contact sheet) is made to hold the lubricant, in order to reduce friction resistance of the pressuring roller and a pressing member pressuring the pressuring roller to the fixing belt. The sliding contact sheet is attached so that a center sliding contact portion thereof is interposed between the pressing member and the pressuring roller and an end portion thereof is wound around the pressing member.
Incidentally, inside the fixing device, the heat source heating the fixing belt at an opposite side to a contact position with the pressuring roller, and a supporting member supporting the fixing belt. The fixing belt is heated by the heat source. Temperature of the fixing belt does not exceed 200 degrees centigrade at the contact position with the pressuring roller, but the fixing belt becomes high temperature at a heated position at the opposite side. The supporting member is arranged at the opposite side (a heated side) to the contact position of the fixing belt and the pressuring roller, with respect to the pressing member. Because the supporting member is made of metal or the like in order to secure strength, the supporting member is heated to high temperature (e.g. 250 degrees centigrade or more) by the heat source. Therefore, the sliding contact sheet is heated at a side of the end portion wound around the pressing member rather than a side of a sliding face.
Because the lubricant held by the sliding contact sheet is made of silicon-based or fluorine-based heat-resistant oil or grease, the lubricant has a quality of evaporating when it exceeds 250 degrees centigrade. Because the lubricant is used so that the sheet is impregnated with the lubricant, if a part of the lubricant becomes high temperature, the whole lubricant becomes high temperature by transmission of temperature rise, and then, it is feared that the lubricant is dried up by evaporating. Subsequently, if the lubricant is dried up, it is feared that friction resistance of the sliding contact sheet and the fixing belt is increased, and then, malfunction of the fixing belt, such as increase of load torque and rotation failure, is caused.